Two different questions on naval technology

[Todjaeger]

Hello All, I have two different questions on Naval technology.

The first question is with regards to naval radar. Some vessels I've seen have an air/surface search radar, other vessels have separate air search and surface search radars. What I'm wondering is if there is a general rule about performance differences? In other words, does a dedicated surface search radar detect surface craft better than a combination air/surface search, or is it basically the same performance?

The other question I have regards delivery systems for lightweight torpedoes from surface vessels. Systems like Ikara and ASROC have been used for standoff torpedoe delivery. How useful are such systems really? From what I've seen in terms of ship deployment, Ikara has been phased out, and ASROC seems on the way out.

-Cheers

 

[Big-E]

Hello All, I have two different questions on Naval technology.

The first question is with regards to naval radar. Some vessels I've seen have an air/surface search radar, other vessels have separate air search and surface search radars. What I'm wondering is if there is a general rule about performance differences? In other words, does a dedicated surface search radar detect surface craft better than a combination air/surface search, or is it basically the same performance?

The other question I have regards delivery systems for lightweight torpedoes from surface vessels. Systems like Ikara and ASROC have been used for standoff torpedoe delivery. How useful are such systems really? From what I've seen in terms of ship deployment, Ikara has been phased out, and ASROC seems on the way out.

-Cheers

Surface search and air search are different modes or different radars altogether depending on the system. Surface search is extremely limited in range and has a lower angle of elevation to pick up targets. Air search has greater range because you are looking at higher elevations which extend the viewing capabilities.

The use of ASROC is particularly limited to detection range of the searching vessel. If she doesn't have a helo then it is only useful to give the torpedeo a range boost so the evading sub has no means of outrunning the torp. ASROC really is obsolete if you have ASW aircraft to extend range and strike capabilities of an ASW ship. Without the helo range an Akula with 63cm torp will outrange and outrun and sink any ASW ship with only ASROC... the hunter will have become the hunted.

 

[EnigmaNZ]

I think it has to do with the different target types, and is the best frequency to employ. You might use a frequency that is a good compromise, cutting costs of 2 separate systems. For a corvette or frigate built on a budget this will suffice. But if you intend putting them in harms way and the money is available, then you'd go for separate systems. Very high frequencies give a return that contains a lot of information that allows you to identify aircraft type, etc, a bit like a high resolution photograph, idea for air search, or close targets, low frequencies have the advantage of being able to be bounced off the ionosphere increasing range, but have a lower resolution. With the advent of stealth aircraft in the west, the chinese for example, have fitted meter wavelenght YAGI antenna to their new AAW destroyer (052C) which is supposed to be able to see through the stealth. I think the ukrainians came up with the technolgy. The americans have come up with a ship based radar that has a decent range while being so low powered it should be undetectable. But I am no expert, so no flames please if I have boobed somewhere lol, just an enthusiastic amature

 

[contedicavour]

At least in the Italian Navy we try to separate systems : RAN 10"S"-frequency for surface search and RAN-40L or EMPAR D-band for air search. Though there is a combined system for lighter vessels or fleet oilers which is the RASS.

Regarding systems like ASROC, together with France, Italy has developed a modified version of Teseo Mk2 SSM capable of launching torpedoes up to 40km away from the ship (called MILAS launching MU90 torpedoes). Given the number of EH-101s and AB212 (soon NH90) in service from all our DDG, FFG, OPVH, we make full use of such systems because we try to pick up enemy SSKs as far away as possible.

cheers

 

[Todjaeger]

Okay, doesn't seem I was clear about the radar, at least in terms of what I was trying to find out. In general cases, does the air search mode of an air/surface search radar equal a dedicated air search radar? Same question again for surface search mode compared to a dedicated surface search radar. Basically what I'm trying to determine is if compromises made to allow a radar to conduct dual air and surface searches have a negative impact on performance, compared to separate arrays each doing either air or surface search.

From what I understand, phased arrays like SPY-1, EMPAR are an entirely different kettle of fish.

Thanks Conte for the info on MILAS, I hadn't heard of that program. So now I know that systems like ASROC are still in use/development. Are there any plans on developing MILAS so that is can be used against surface targets? Or is the MU-90 torpedoe not considered large enough?

 

[contedicavour]

Okay, doesn't seem I was clear about the radar, at least in terms of what I was trying to find out. In general cases, does the air search mode of an air/surface search radar equal a dedicated air search radar? Same question again for surface search mode compared to a dedicated surface search radar. Basically what I'm trying to determine is if compromises made to allow a radar to conduct dual air and surface searches have a negative impact on performance, compared to separate arrays each doing either air or surface search.

From what I understand, phased arrays like SPY-1, EMPAR are an entirely different kettle of fish.

Thanks Conte for the info on MILAS, I hadn't heard of that program. So now I know that systems like ASROC are still in use/development. Are there any plans on developing MILAS so that is can be used against surface targets? Or is the MU-90 torpedoe not considered large enough?

On the 1st item, I've heard from Navy officers that the answer is yes, having separate systems improves performance (especially as it allows for simultaneous reading instead of having to switch from one mode to another).

On the 2nd item, Mu90 is a light torpedo which is an evolution of your Mk46 so it is too light to be used against big surface ships. We did have heavy torpedoes A180 Whitehead aboard our ASW FFGs, but we took them off. For ASUW our Teseo Mk2S already have 180+ km range, so no need for torpedoes as a complement.

cheers

 

[Sea Toby]

Ascroc and Ikara missile ranges were only like 5-6 miles, ASW helicopters have a range ten times larger. No wonder why they are being phased out.

In the US Navy front line warships in a carrier battle group have separate air search and surface search radars. However, many of the warships in the background don't, as you noticed these ships have a combined air search and surface search radar.

 

[Wooki]

Hello All, I have two different questions on Naval technology.

The first question is with regards to naval radar. Some vessels I've seen have an air/surface search radar, other vessels have separate air search and surface search radars. What I'm wondering is if there is a general rule about performance differences? In other words, does a dedicated surface search radar detect surface craft better than a combination air/surface search, or is it basically the same performance?

All radar use electromagentic energy and because of that, if you put a radar in space (where there are no gravitational influences) your radar sweep would look like a torus, or donut.

As soon as you put your radar at the bottom of a gravity well (earth) then the torus splits up into "lobes".

You tune those lobes either physically or by electronic means to enhance performance in a desired "space" e.g. surface radar is tuned to look for targets close to the surface of the earth, as shown in my little sketch.

So, for example; I had a funny feeling one morning, so before my watch I shimmied up the radar mast and physically retuned the radar so that it's primary lobe would touch the water's surface at 18NM. I then set the computer monitoring the radar to look for targets over 100knots in speed at 18NM.

2 hours into my watch the Chinese fired a friggin missile at us and the radar picked it up in plenty of time for lots of alarms and bells and little blinking lights to go off, giving me time to take a last sip of my tea, (I like tea) put down my cup and turn into the threat. Luckily for us it splashed down before it hit.

Radars aren't mysterious things.

Energy is also not "reflected" as people often think. Its more accurate to say it is resonated from a target. In other words all materials absorb "x" or "y" amount of radiation before they begin resonating the radar energy. So, if you want to create a "stealth" ship, just don't paint it, as rust absorbs a lot of electromagnetic energy before it begins to resonate.

Its also one reason why russian spy trawlers are very hard to pick up on radar

cheers

w

 

[Big-E]

Nice drawing... at first I thought it was a potted plant.

 

[Wooki]

Nice drawing... at first I thought it was a potted plant.

ahh shucks, thanks Big E. I guess it is because I have an aloe plant on my desk.

cheers

w

 

[Grand Danois]

So, Wooki, you seem to know this stuff. How about a little lesson for dummies on passive vs active arrays.

You may include tea, Chinese or Chinese tea again.

Cheers.

 

[Wooki]

So, Wooki, you seem to know this stuff. How about a little lesson for dummies on passive vs active arrays.

You may include tea, Chinese or Chinese tea again.

Cheers.

No I don't, I just get occassional funny feelings, sleep walk and draw potted plants.

Active transmits and Passive receives (to answer your question). If you want passive to work well, you need multiple receivers at different locations. Like they do with radio astronomy (for example).

Thats one of the reasons that ship to ship free space laser communications would be useful as you could make one v/l the master and then every 50 micro seconds or so check everyone's clock via the laser comm... among other things. Save space too.

cheers

w

 

[Grand Danois]

Oh dang! I wasn't specific enough. I was thinking of passive vs active electronically scanned arrays.

But you do write those kinda posts That's also why you got asked.

I will go have a look at what free space laser based comms are.

Cheers

Edit: A-ha! Science toys you can make with your kids, hehe. Not that it makes me see the connection.

 

[Wooki]

Oh dang! I wasn't specific enough. I was thinking of passive vs active electronically scanned arrays.

But you do write those kinda posts That's also why you got asked.

I will go have a look at what free space laser based comms are.

Cheers

Edit: A-ha! Science toys you can make with your kids, hehe. Not that it makes me see the connection.

electronic scanning is basically tuning the lobes electronically. Which means you can look in any direction you want without having to physically move the array. The more Tx nodes you have the more space you can look at until you get a 3D "real time" picture.

All radars operate active and passive... you transmit and then you stop transmitting so you can "listen". so "active" really means a passive system that is transmitting some of the time.

"Passive" is when you are just sitting there listening. That requires a huge amount of computing power as you want to listen over a broad frequency band and your Rx also needs to be able to handle that.

Free space laser comms are just using laser comm links through the atmosphere. Tera Hertz frequencies are the best for that.

cheers

W

 

[Grand Danois]

Alright. I got it.

Cheers

 

[Todjaeger]

Okay, just let run through this so I can make sure I understand it properly.

Air search, the aperture of the radar is more or less angled upwards so that the radar returns will be coming from aircraft above the horizon.

With the surface search, the aperture is aimed downward, so that the edge of the horizon is the limit to the search area.

Now with an air/surface search radar, the aperture shifts between scans from the surface search angle to the air search angle. To me, that almost sounds like a synthetic aperture radar.

With dedicated air and surface search radars, the two antennae are operating at the same time, each doing it's own particular search.

Have I got it more or less correct?:unknown

-Cheers

 

[EnigmaNZ]

The difference between AESA and PESA

In a passive electronically scanned array (PESA), the microwave feed network in the back of the antenna is powered by a single RF source (magnetron, klystron, TWT, etc.), sending its waves into phase shift modules (usually digitally-controlled), which, in turn, feed the numerous emitting elements.

An AESA, instead, has an individual RF source for each of its many transmit/receive elements, making them "active".

This provides for a graceful degradation, so that many T/R modules may fail and the radar would not stop functioning.

Furthermore, AESA radars do not have an RF source in the common meaning of the term (magnetron/klystron/TWT), which usually requires extremely high operating voltages (reaching 50 kVa). Instead of any of the aforementioned traditional RF sources, individual AESA elements create electromagnetic waves through such objects as gallium-arsenide modules which usually require no more than 40 to 60 volts.

I believe thats what you were looking for. The newer APAR and SAMPSON are AESA, while the older SPY is PESA, but the DDX will have the SPY3 which is AESA. from what I understand, the Tico have 2 microwave sources for the separate arrays on the bridge faces and the hanger faces while the Burke has 1 source with all 4 arrays mounted together, so if the one source on the Burke stops working, she has lost her SPY system, on the Tico the lost of 1 source knocks out either front and one side array or rear and other side array, on the Sampson and APAR used on the european ships, each array has a multitude of sources so degradation is gradual.

An analogy, pesa is like a bank of microwave ovens with 1 magnetron supplying all the ovens through waveguides, take out the magnetron and you take out the bank of ovens, aesa is a bank of microwave ovens each with it's own magnetron, take out 1 or more magnetrons and you still have some working ovens. Substitute radar arrays for ovens.

http://en.wikipedia.org/wiki/Active_Electronically_Scanned_Array

 

[Grand Danois]

The difference between AESA and PESA

In a passive electronically scanned array (PESA), the microwave feed network in the back of the antenna is powered by a single RF source (magnetron, klystron, TWT, etc.), sending its waves into phase shift modules (usually digitally-controlled), which, in turn, feed the numerous emitting elements.

An AESA, instead, has an individual RF source for each of its many transmit/receive elements, making them "active".

This provides for a graceful degradation, so that many T/R modules may fail and the radar would not stop functioning.

Furthermore, AESA radars do not have an RF source in the common meaning of the term (magnetron/klystron/TWT), which usually requires extremely high operating voltages (reaching 50 kVa). Instead of any of the aforementioned traditional RF sources, individual AESA elements create electromagnetic waves through such objects as gallium-arsenide modules which usually require no more than 40 to 60 volts.

I believe thats what you were looking for. The newer APAR and SAMPSON are AESA, while the older SPY is PESA, but the DDX will have the SPY3 which is AESA. from what I understand, the Tico have 2 microwave sources for the separate arrays on the bridge faces and the hanger faces while the Burke has 1 source with all 4 arrays mounted together, so if the one source on the Burke stops working, she has lost her SPY system, on the Tico the lost of 1 source knocks out front and one side array, on the Sampson and APAR used on the european ships, each array has a multitude of sources so degradation is gradual.

http://en.wikipedia.org/wiki/Active_Electronically_Scanned_Array

Yes, that is also just about how far I've gotten I my own search.

http://www.defencetalk.com/forums/showthread.php?p=66904#post66904


But I was really looking for what it meant performance wise on the signal processing side of it. How does an AESA offer better detection of LO, filter clutter etc.

Cheers

 

[Wooki]

Okay, just let run through this so I can make sure I understand it properly.

Air search, the aperture of the radar is more or less angled upwards so that the radar returns will be coming from aircraft above the horizon.

With the surface search, the aperture is aimed downward, so that the edge of the horizon is the limit to the search area.

Now with an air/surface search radar, the aperture shifts between scans from the surface search angle to the air search angle. To me, that almost sounds like a synthetic aperture radar.

With dedicated air and surface search radars, the two antennae are operating at the same time, each doing it's own particular search.

Have I got it more or less correct?:unknown

-Cheers

yes

now you are ready to make the quantum leap into RF emitting chips, eh?

cheers

W

 

[Todjaeger]

yes

now you are ready to make the quantum leap into RF emitting chips, eh?

cheers

W

Working on it, working on it... I'm fairly light I mean bright, so I think I could make that quantum leap... Argh. Physics jokes...

-Cheers